The invention relates to a halogen-free, water-blown, flame-retardant rigid polyurethane foam and to a process for its production, and also to the use of oxalkylated alkylphosphonic acids for producing rigid polyurethane foams of this type.
Rigid polyurethane foams are used in many sectors, for example in the refrigeration industry, as insulating materials for construction, for example for heating units or composites, as packaging, and generally as industrial insulation. Rigid polyurethane foams generally have to be provided with flame retardants in order to achieve the high fire-protection requirements desirable in these sectors and sometimes required by legislation. A wide variety of different flame retardants is known and commercially available for this purpose. However, there are often considerable technical problems and toxicological concerns restricting the use of these flame retardants.
For example, when solid flame retardants such as melamine, ammonium polyphosphate or ammonium sulfate are used there are technical problems with metering which frequently necessitate complicated rebuilds or modifications of foaming plants.
Halogen-free flame retardant systems are preferred in principle for reasons of environmental toxicity, and also due to their better performance in terms of the smoke density and smoke toxicity associated with fires.
For flexible polyurethane foam systems, hydroxylated oligomeric phosphoric esters (DE-A-43 42 972) can be used as flame retardants. It is known that these compounds and their properties and effects cannot be similarly used in rigid polyurethane foam systems.
Although in principle flexible and rigid polyurethane foam systems may have approximately the same density and composition, flexible polyurethane foams have only slight crosslinking and exhibit only a low level of resistance to deformation under pressure.
In contrast, the structure of rigid polyurethane foams is composed of highly crosslinked units, and rigid polyurethane foam has very high resistance to deformation under pressure. A typical rigid polyurethane foam is of closed-cell type and has low thermal conductivity.
During the production of polyurethanes, which proceeds via the reaction of polyols with isocyanates, it is primarily the nature and chemistry of the polyol (functionality) which affects the subsequent foam structure and the properties of this material.
It is an object of the present invention to provide a halogen-free, water-blown, flame-retardant rigid polyurethane foam which does not have the abovementioned disadvantages and meets the necessary and prescribed requirements for flame retardancy, ease of production, low smoke density and low smoke toxicity.
The abovementioned object is achieved by means of a polyurethane foam of the type mentioned at the outset, which comprises oxalkylated alkylphosphonic acids as flame retardant.
The oxalkylated alkylphosphonic acids preferably have the formula I 
where
R1 is a methyl, ethyl or propyl radical,
R2 and R3 are identical or different and are a methyl, ethyl or propyl radical and x is a number from 1.2 to 1.9.
It is preferable for R1 to be a methyl radical, and x a number from 1.5 to 1.7. The value for x is the average chain length.
The halogen-free, water-blown, flame-retardant rigid polyurethane foam preferably comprises, based on the fully cured rigid polyurethane foam, from 0.1 to 30% by weight of the flame retardant.
The halogen-free, water-blown, flame-retardant rigid polyurethane foam particularly preferably comprises, based on the fully cured rigid polyurethane foam, from 5 to 20% by weight of the flame retardant.
The halogen-free, water-blown, flame-retardant rigid polyurethane foam preferably has a density of from 25 to 80 kg m3.
It particularly preferably has a density of from 30 to 50 kg m3.
The abovementioned object is also achieved by means of a process for producing halogen-free, water-blown, flame-retardant rigid polyurethane foams, which comprises using oxalkylated alkylphosphonic acids as flame retardant.
The oxalkylated alkylphosphonic acids preferably have the formula I 
where
R1 is a methyl, ethyl or propyl radical,
R2 and R3 are identical or different and are a methyl, ethyl or propyl radical and x is a number from 1.2 to 1.9.
The process is preferably executed by reacting organic polyisocyanates with compounds having at least two hydrogen atoms capable of reaction with isocyanates, with water as blowing agent, with stabilizers, with activators and/or with other conventional auxiliaries and additives, in the presence of oxalkylated alkylphosphonic acids of the formula I.
The oxalkylated alkylphosphonic acids of the formula I are preferably compounds liquid at processing temperature. For the purposes of the present invention, processing temperature is the temperature at which the starting components are mixed.
The oxalkylated alkylphosphonic acids of the formula I are preferably compounds reactive toward isocyanates.
The amount of the oxalkylated alkylphosphonic acids used of the formula I is preferably from 0.01 to 50 parts, based on 100 parts of polyol component.
The amount of the oxalkylated alkylphosphonic acids used of the formula I is particularly preferably from 10 to 35 parts, based on 100 parts of polyol component.
The invention also provides the use of oxalkylated alkylphosphonic acids of the formula I as halogen-free flame retardant for producing flame-retardant rigid polyurethane foams.
Regarding the rigid polyurethane foams:
These are mainly foams having urethane groups and/or isocyanurate groups and/or allophanate groups and/or uretdione groups and/or urea groups and/or carbodiimide groups. The use according to the invention preferably takes place during the production of polyurethane foams or of polyisocyanurate foams.
The materials used for producing the isocyanate-based foams are: Starting materials: aliphatic, cycloaliphatic, araliphatic, aromatic or heterocyclic polyisocyanates (see, for example, W. Siefken in Justus Liebigs Annalen der Chemie, 562, pp. 75-136), for example those of the formula Q(NCO)n, where n=from 2 to 4, preferably from 2 to 3, and Q is an aliphatic hydrocarbon radical having from 2 to 18 carbon atoms, preferably from 6 to 10 carbon atoms, a cycloaliphatic hydrocarbon radical having from 4 to 15 carbon atoms, preferably from 5 to 10 carbon atoms, an aromatic hydrocarbon radical having from 6 to 15 carbon atoms, preferably from 6 to 13 carbon atoms, or an araliphatic hydrocarbon radical having from 8 to 15 carbon atoms, preferably from 8 to 13 carbon atoms, for example the polyisocyanates described in DE-A-28 32 253, pp. 10-11. Particular preference is generally given to the polyisocyanates readily available industrially and derived from tolylene 2,4- and/or 2,6-diisocayanate or from diphenylmethane 4,4xe2x80x2- and/or 2,4xe2x80x2-diisocyanate.
Other starting materials are compounds having at least two hydrogen atoms capable of reaction with isocyanates, with a molecular weight of from 400 to 10,000 (xe2x80x9cpolyol componentxe2x80x9d). For the purposes of the present invention, these are compounds having amino groups, thio groups or carboxyl groups, and preferably compounds having hydroxyl groups, in particular from 2 to 8 hydroxyl groups, and specifically those of molecular weight from 1000 to 6000, preferably from 2000 to 6000, and are generally polyethers or polyesters dihydric to octahydric, preferably dihydric to hexahydric, or else polycarbonates or polyesteramides, as known per se for the production of homogenous or of cellular polyurethanes, and as described in DE-A 28 32 253, for example. The at least dihydric polyethers and polyesters are preferred according to the invention.
Other starting materials which may be used if desired are compounds having at least two hydrogen atoms capable of reaction with isocyanates and with a molecular weight of from 32 to 399. In this case, again, for the purposes of the present invention these are compounds having hydroxyl groups and/or amino groups and/or thio groups and/or carboxyl groups, preferably compounds having hydroxyl groups and/or amino groups, and serving as chain extenders or crosslinkers. These compounds generally have from 2 to 8, preferably from 2 to 4, hydrogen atoms capable of reaction with isocyanates. Examples of these are again described in
DE-A-28 32 253.
If desired, concomitant use is made of auxiliaries and additions, such as catalysts of the type known per se, surface-active additives, such as emulsifiers and foam stabilizers, reaction inhibitors, e.g. substances of acid reaction, such as hydrochloric acid or organic acid halides, or else cell regulators of the type known per se, such as paraffins or fatty alcohols, and dimethylpolysiloxanes, or else pigments or dyes, or other flame retardants, or else stabilizers to counteract aging or weathering, core-discoloration inhibitors, plasticizers or fungistatic or bacteriostatic substances, or else fillers, such as barium sulfate, kieselgur, carbon black or whiting
(DE-A-27 32 292).
Pages 104 to 123 of Kunststoff-Handbuch [Plastics Handbook], Vol. VII, Carl Hanser Verlag, Munich, 1993 describe further examples of surface-active additives and foam stabilizers which may, if desired, be used concomitantly according to the invention, and also cell regulators, reaction inhibitors, stabilizers, flame-retardant substances, plasticizers, dyes and fillers, and also fungistatic or bacteriostatic substances, together with details of the manner of use of these additions, and of their manner of action.
Polyisocyanurate foams are produced using the processes and conditions known for this purpose.